1. Field of the Invention
The present invention is related to an organic EL (electroluminescence) display device and a method for manufacturing the device. Especially, the present invention is related to an organic EL display device and a method for manufacturing the device, in which the device has no display defect and has improved durability by forming a second electrode covering the entire surface of an inorganic material pattern.
2. Description of the Related Art
An organic EL element emits light when a current is supplied to a light emitting layer which is formed from an organic light emitting material and between two opposed electrodes. In order to manufacture an element of high efficiency and high reliability, a film thickness of the light emitting layer is important factor. In the case of forming a color display using the organic EL element, it is necessary to perform patterning on the organic EL element with high definition.
Low molecular materials and polymeric materials are examples of organic luminescent materials that can be used to form the organic luminous layer. Generally, as for low molecular materials, thin film can be formed by vacuum evaporation. A mask with minute patterns is used at this time, and patterns are formed. In a manufacturing method with the use of vacuum processing such as vacuum evaporation, upsizing of a substrate can diminish the accuracy of the patterning. In addition, throughput is low because a layer is formed in vacuum.
Thus the following method is tried recently. Polymer organic luminescent material is dissolved in a solvent, and ink is made. This ink is used, and thin film is formed by a wet coating method.
A layer structure of an organic light emitting medium layer when an organic light emitting medium layer including an organic light emitting layer is formed by wet coating using coating solution of high polymer materials is described below. The two-layer construction in which a hole transport layer and an organic light emitting layer are laminated on an anode side is generally used. As for the organic light emitting layer, it is necessary for the organic light emitting inks including organic light emitting materials of red (R) green (G) and blue (B) in a solvent to be separately applied in order to form a color panel.
However, separated application of materials other than light emitting materials is not generally performed. Thereby, a solid film as a common layer for all colors is sufficient. High definition patterning is not necessary. Then, in order to form a hole transport layer, polymer is formed by a wet coating method, a low molecular organic material is deposited by a vacuum vapor deposition method, or a film made from an inorganic material is formed by a vacuum vapor deposition method, a sputtering method, a CVD method or other film formation methods. Among them, especially in the case of an inorganic material, there are problems in which a composition ratio or a structure of an inorganic material changes when an inorganic material is dissolved in water or is oxidized.
In order to solve this problem, bad influence is reduced by sealing a device (an organic EL element) in an inactive gas under a condition where an amount of moisture or oxygen is strictly controlled. However, reaction by remaining moisture or oxygen in gas occurs. Thereby, non-light emitting area called dark spots is generated. So, this process is insufficient. Especially, reaction occurs in a place where the place is not covered by other film, and the reaction reaches a display region.
In a patent document 1 (JP 2824411 B2), a technology in which a metal oxide is used for an inorganic material is disclosed.
As shown in FIG. 6, a conventional organic EL display device 400 includes, for example, an inorganic hole transport layer 33, an organic light emitting layer (not illustrated in figures) and a counter electrode 32 on a display region 30 in which a plurality of pixel electrodes 31 are provided. Among them, in the case where a hole transport layer 33 including an inorganic hole transport material is formed on a display region 30, pattern of a hole transport layer 33 is formed by a vacuum vapor deposition method, a sputtering method, a CVD method or the like, in which a shape of the pattern is a shape except for a place of a driver IC, a contact part of a counter electrode 32, an adhesive part for a sealing member and the like. Thereafter, a pattern of a counter electrode 32 is formed. At this time, the pattern of a counter electrode 32 is as follows: the pattern of a counter electrode 32 is different from a pattern of an inorganic hole transport layer 33; and a pattern of a hole transport layer 33 is larger than a pattern of a counter electrode 32, in which a hole transport layer is used as an insulating film under a counter electrode 32 in order to prevent short-circuit between a counter electrode 32 and pixel electrode 31 arranged on a substrate from occurring. In these cases, there is region where a hole transport layer 33 is not covered.
The following problem was found: as shown in FIG. 7, a part where a hole transport layer 33 is not covered by a counter electrode 32 reacts with oxygen or moisture 37; the reaction region reaches a display region 30 at early time; and this causes non-light emitting part called dark spots. Especially, in the case of an inorganic hole transport layer by which EL characteristics are found to be improved, it was found that this problem is remarkable.
An object of the present invention is to provide an organic EL display device and a method for manufacturing the device, in which display defects (display failures) do not occur and durability is improved because dark spots are not generated. This is because a film surface and an end part of an inorganic layer do not react with oxygen or moisture by forming a second electrode covering the entire surface of a film using an inorganic material.